The potential advantages of carbon dioxide over room air to insufflate the bowel during colonoscopy include its nonexplosive nature and rapid absorption. To evaluate whether this rapid absorption would minimize any reduction in colonic blood flow resulting from the distention, we measured inferior mesenteric artery flow before, during, and after insufflation of the canine colon with room air and carbon dioxide under conditions of transient and constant elevations of intraluminal pressures. Intraluminal pressures remained elevated for briefer periods after carbon dioxide administration, and blood flow was far less compromised. At lower levels of transient (40 mm Hg) and constant (60 to 70 mm Hg) intraluminal pressure elevation, colonic blood flow was actually increased. Because it is nonexplosive and rapidly absorbable and interferes only minimally with colonic blood flow, carbon dioxide is the preferable agent to use during colonoscopy, especially in patients with suspected or proven colon ischemia in whom prolonged distention and diminished blood flow are to be avoided.